Valve bags, such as for carrying powder, grain, cement, animal foodstuffs, etc., are widely known. A typical valve bag is formed of thick paper having a stitched top and a valve formed in the side of the bag. The valve is opened and impaled onto a chute tube through which material is conveyed into the bag. The bag is effectively self-sealing, as once it has been removed from the chute tube, the valve closes, therefore, preventing the contents of the bag from escaping through the valve.
Disadvantages of the bag described above are the lack of resistance to moisture, such as rain or humidity, and tendency to tear.
Plastic valve bags, and a method and apparatus for making them, are also known. For example, U.S. Pat. No. 6,890,290 (Amplas) discloses a valve bag wherein a film web is formed into a continuous tube, and the tube is sealed internally by a device which is disposed within the tube of material.
The valve bag disclosed in U.S. Pat. No. 6,890,290 is more resistant to moisture and damage such as tearing than a thick paper valve bag. However, the method of forming the bag is complex, and the required equipment is expensive. Therefore, it is only commercially viable to use this method of forming a valve bag for certain applications.
Valve bags are currently used for fairly large quantities of material, and not for small quantities of discrete parts such as nuts, bolts or spare parts. The use of current valve bags for such small quantities is not economical due to the cost of equipment. The use of paper valve bags could also lead to damage of the items by moisture, or the parts themselves could cause damage to a paper valve bag. Therefore, small quantities of discrete parts are usually packaged in bags which must be further sealed after the contents have been put into the bag.